I swear by Coda. I've used Dreamweaver for quite a long time, since it was the most complete editor there was (as far as I knew). There is a PHP debugger (which someone else in this thread said there wasn't, you just have to set it up (sites)), good highlighting, auto-completion and good HTML editing.
Then someone said that I should try Coda. The first moment I felt in love. Its simplicity is really lovely. Not many boxes like Dreamweaver, you just add one project (site) and that's it. Easy coding without too much stuff you don't need, but unlike TextMate (which I also tried for some time) it is more user friendly. I missed the PHP debug, but then I found a plugin which could do it. There are many more plugins as well! The only thing that I miss is auto-completion for custom variables, but I hope that will come next version!
Anyway, what you like is really up to you. Each program has a trial version, even Dreamweaver, so if I were you, just use them for a week and see which one you really prefer.